Duplex telegraph



(No Model.)

DUPLEX TBLBGRAPH.

N0. 258,636. Patented May 30, 1882.

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JOSEPH E. FENN, OF ELIZABETH, NE JERSEY.

DUPLEX TELEGRAPH.

SPECIFICATION forming part of Letters Patent No. 258,636, dated May 30, 1882.

Application tiled January 5, 1882. (No model.) I

To all whom it may concern y Be it known that I, JOSEPH E. FENN, of Elizabeth, county of Union, and State of New Jersey, have made an Improvement in Telegraph Apparatus i'or Simultaneous' Transmission in Opposite Directions, of which the following is a description, reference being had to the accompanying drawing.

I have discovered in the transmission of messages that after a signal has been completed upon the receiving-instrument at a distant station, and after the battery has been disconnected from the main line at the transmittingstation, a secondary current of momentary duration will be set up throughout the main-line circuit in the same direction as the primary current of charge, occurring with and duc to the demagnetization of the receiving-instrument at the distant station. This secondary current, having its origin at the distant station, will obviously energize the receiving-instrument at the transmitting-station. Thus by and accompanying the transmission ot signals to a distant station will the receiving-instrument at the home station be actuated to give false signals in violation ot' the essential condition ofa telegraph system for the simultaneous transmission ot' messages over a single line in opposite directions, which is that the operation of the transmitting apparatus shall not cause signals to be made upon its associate receivinginstrument. The strength of the momentary secondary current is proportional ofcourse to the amount ot' magnetism discharged from the receivin g-magnet, and isinversel y proportion al to the electrical resistance ofthe line. I have therefore found where several electro-magnetic receivers, asin a quadruplex or sextuplex system, are employed at one station, and Where the mainline haslittleelectrical resistance,that the strength ot' the secondary current will be sufficiently strong to cause the mutilation of signals upon the receiviiig-instrument at the home station.

In the accompanying drawing, A and B represent terminal stations, at which the apparatus of one is similar to that of the other.

R is an ordinary differential relay, having oppositely-wound coils m and y, forming parts, respectively, of the main and artiiieial lines.

L and H are the main and artificial lines,

coming together at o and connecting with key K, which, when open, connects the line to earth through a back contact with point 2, and when The artiiicial As the apparatus of one station is similar to that of the other, devices at station B need not be specifically described.

I will now describe the operation of my invention.

When key K is depressed and battery B is thereby connected to line the current divides a-nd acts oppositely upon relay R, and, owing to the agency ofcondenser C, no false signal upon relay R will be made, either by the direct action ot' the current sent to line or by the effects ot staticinduction upon the line; but upon completion of a signal sent from station A and at'- tcr removal of battery B i'rom the line the core of' relay R at station B will discharge its'magnetism, and thereby cause alseeondary current to be set up iroin earth, through coil x at station A, main line L, and coil m at station B to earth, of the same polarity as that from battery B, employed in transmitting thc signal. The polarity of this secondary current is opposite and subsequent to that of the static discharge ot' the main line at station A, and is therefore uncompensated by the action ot' condenser G, The secondary current acts upon the relay at A to produce a false signal as it passes only through coil x on its way to earth. To compensate the action of the secondary current, having its origin in the relay of station B upon relay R ot' station A, I develop an articial secondary current in the artificial line at station B, which acts over the artificial line and through coil y ofthe relay, in point of polarity, time, and quantity, in the same manner as does the main line secondary current through coil m. To develop such a current I IOO employ a series of electro-magnets whose coils, one or all, may be inserted in the artificial line, and between these coils and the differential relay is placed a resistance equal or proportional to that of the main line. The secondary currents in the artificial and main-line coil are of the same polarity as those ot' the currents ot' charge from thc battery, and will therefore neutralize each other. The resistance of the artificial line must be placed between the relay and the colnpensating electromagnets to cause the secondary currents to act upon the relay simultaneously. Otherwise, instead of' preventing one f'alse signal, two others wlll be produced. I employ one or all of' the electromagnets in lthe artificial line, according as there are one or more receivingrelays in line at the distant station.

Instead of employing a series of inductionmagnets, some of which may be shunted from the artificial line, I may use any of the well knownformsofelectro-magneticdevices,wherebythe currents of induction produced therein may be varied in strength and time ot' discharge. InA all eases it is necessary to put the induction-magnets in the artitieial or compensating circuit or branch with a resistance proportional to that ot' the line between the relay and induction magnets. In a dit'ereir tial system said intervening resistance must equal that ot' thc mainline. In the bridge sys tem it need not be equal, but should be proportional thereto.

For convenience I have shown only one receiving-relay at each station, as in a duplex, though I do not limit myself in this respect. In quadruplex or sextuplex telegraphy several relaysare necessary' at one station.

What I claim, and desire to secure by Letters Patent, is-

1. The method of preventing the extra current upon a telegraph-line, set up by receivinginstruments at distant stations, from producing false signals upon the receiving-instrumenty at the home station in the process of transmitting signals therefrom, which consists in the simultaneous production at the home station of an artificial extra current capable of exerting an effect substantially equal but opposite to that due tothe distant instrument set up in the main line upon the receiving-instrument at the home station.

2. In a telegraph system, for simultaneous transmisson in opposite directions, the coinbination, at each and both terminal stations, ot' transmitting devices, duplex receiving-instruments, and an artificial line having a resistance proportional to that ofthe main line, and electro-magnetic induction apparatus, said resistance being located upon the artificial line between the receivingdnstrument and the induction-magnets, as specified.

3. In a telegraph system for simultaneous transmission, the combination, at cach station, of duplex receiving-instruments, and an artificial line,having an adjustable electro-magnetic device, substantially as specified, and a resistance proportional to that of the main line, situated between the rcceiving-instruments and the electro-magnetic devices, for the purpose set forth.

Executed by me this 29.h day of December, 1881.

JOSEPH E. FENN.

Witnesses:

JOHN C. SANDERS, WM. ARNOUX. 

